1. Field of the Invention
The present invention relates to a substrate for liquid discharge head that discharges liquid such as ink, and a manufacturing method for a liquid discharge head.
2. Description of the Related Art
A head (inkjet head) used for an inkjet recording typically includes a plurality of discharge ports, a liquid flow path communicating with the discharge ports, and an electrothermal transducer that generates thermal energy used for discharging an ink.
In a heat-acting portion of an inkjet head (hereinafter, simply referred to as a head) that causes heat to act on the ink, a phenomenon may occur, in which a coloring material and additives and the like contained in the ink may be decomposed on the molecular level by heating at a high temperature and changed to a hard-dissoluble substance, and be physically adsorbed on an upper protective layer as a burnt deposit.
To solve the above-described problem, U.S. Patent Application Publication No. 2007/0146428 discusses a technique for removing the burnt deposit, by forming an upper protective layer containing metal such as iridium (Ir) or ruthenium (Ru) on a heat-acting portion that contacts the ink, applying a voltage onto the upper protective layer to perform an electrolytic reaction, thus dissolving the upper protective layer. Further, the upper protective layer is formed via a protective layer and an adhesive layer, and the adhesive layer is also used as a wiring when a voltage is applied onto the upper protective layer.
Japanese Patent Application Laid-Open No. 2007-230127 discusses a method for performing electrolytic reaction (electrolytic etching) using an electrolytic solution, in order to arrange Ir as a hard-etching material on the heat-acting portion.
However, the burnt deposit-removing operation may not possibly be uniformly performed at the adhesive layer, if wiring resistance varies. Further, in order to restrain reaction with the ink, and to enhance adhesiveness with a nozzle material, it is desirable that a surface of the adhesive layer be passivated. In order to achieve both, passivation of the surface of the adhesive layer by making the adhesive layer thick, or by the electrolytic reaction using the electrolytic solution may be useful. However, it is practically difficult to make the thickness of the upper protective layer and the adhesive layer formed on the heating resistor extremely thick, from viewpoint of transmission of heat energy to the ink. Further, it is difficult to cause the passivation by the electrolytic reaction using the electrolytic solution to uniformly react within a wafer plane. This is because, already-passivated area does not further react, and as a result, the voltage rises unevenly, and it is difficult to control the electrolytic reaction.